上诉不加刑原则的本质是被告人权利的保障机制，该原则在一定条件下 限制二审法院加重被告人刑罚以保障其上诉权的行使。上诉不加刑原则在我国正式确立于1979年的《刑事诉讼法》，之后又在该法的历次修订中得以不断完善，司法机关也通过司法解释进一步明确了该原则的适用规则。但我国“重实体，轻程序”的法治传统以及刑事诉讼法所秉承的客观真实原则深刻影响了上诉不加刑原则的司法运用。在上诉不加刑原则确立以来的运行实践中，突出的问题集中于人民法院通过发回重审制度和审判监督程序变相加刑，同时司法机关对被告人滥用上诉权以谋取所谓不正当程序利益的现象也有所担忧。随着上诉不加刑适用规则的不断细化和完善，实践中二审法院利用发回重审变相加刑的做法得到了有效遏制，但该原则与审判监督程序的衔接问题仍是争论的焦点。此外，在检察机关或自诉人提起有利于被告人的抗诉或上诉案件中，二审法院改判加刑并不违反我国现行法律规定，但这一做法缺乏正当性和合理性。认罪认罚从宽制度从2016年开展试点改革到2018年《刑事诉讼法》正式确立以来，一些认罪认罚案件中的被告人既获得了认罪认罚所带来的量刑优惠，又借上诉权以达到“留所服刑”的目的或谋求更为轻缓的裁判结果，由此引发关于上诉不加刑原则客观上鼓励认罪认罚案件被告人滥用上诉权的争论。不可否认，上述问题对上诉不加刑原则的贯彻执行都造成了不小的挑战。面对这一原则在司法适用中所体现出的诸多问题，需明确其保障被告人上诉权的核心价值，厘清其与刑事诉讼中其他相关原则、理念之间的关系，对理论上存在的一些误解予以澄清。在制度设计上，增设上诉不加刑原则在有利于被告人之抗诉或上诉案件中的适用，在认罪认罚案件中引入裁量型上诉制度并在二审中明确上诉不加刑原则的普遍适用，同时限制和完善被告人单方上诉案件在二审后启动审判监督程序的条件，使这一原则的适用进一步规范化、系统化。

The essence of the principle of no additional punishment on appeal is the guarantee mechanism of the defendant's rights. Under certain conditions, this principle restricts the court of second instance to increase the appellant's punishment to protect the defendant's right of appeal. The principle of no additional punishment on appeal in China was officially established in the Criminal Procedure Law of 1979, which has been improved in the previous amendments of the law, and the judiciary authorities have further clarified the applicable rules of the principle through judicial interpretation. However, the legal tradition of "emphasizing substance and neglecting procedure" and the principle of objective reality in the criminal procedure law have a profound impact on the judicial application of the principle of no additional punishment on appeal.In the operation practice of the principle of no additional punishment on appeal, the prominent problems focus on the people's court increasing the punishment in disguise through the remand retrial system and trial supervision procedure. At the same time, the judicial organs also show their concern about the defendant's abuse of the right of appeal to obtain the so-called improper procedural interests. With the improvement of the applicable rules of no additional punishment on appeal, the practice of increasing punishment in disguised form by sending back for retrial has been effectively curbed in practice, but the connection between the principle of no additional punishment on appeal and the trial supervision procedure is still the focus of debate. In addition, in the protest or appeal cases filed by the procuratorate or private prosecutor in favor of the defendant, the second instance court's change of sentence and increase of punishment does not violate the current legal provisions of our country, but this practice lacks validity and rationality. After the pilot reform of the leniency system for pleading guilty in 2016 and the implementation of the newly revised Criminal Procedure Law in 2018, on the one hand, the defendants in some cases of guilty plea and punishment obtained the benefits of sentencing concessions brought by guilty plea and punishment, on the other hand, they took advantage of the right of appeal to realize the judgment results of "staying in detention facility for serving sentences" or seeking a lighter sentence. This phenomenon has triggered a debate that the principle objectively encourages the defendants to abuse the right of appeal. It is undeniable that the above problems have posed great challenges to the implementation of the principle of no additional punishment on appeal. In response to the problems reflected in the judicial application of the principle of no additional punishment on appeal, it is necessary to clarify the core value of the principle to protect the defendant's right of appeal, and clarify the relationship between the principle and other principles or notions, and clarify some misunderstandings in theory. In terms of procedure design, it is suggested to limit and improve the starting conditions of the trial supervision procedure of the defendant's unilateral appeal case, add the application of the principle of no additional punishment in appeal in favor of the defendant's protest or appeal case, introduce the discretionary appeal system in the case of guilty plea and punishment, and clarify the general application of the principle in the second instance, so as to further standardize and systematize the application of the principle of no additional punishment in appeal.